Multi-frequency ultrasonic transducer

Abstract

An ultrasonic transducer consisting of three piezoelectric element couples sandwiched between four metal terminals. Each piezoelectric couple has two piezoelectric elements separated by an electrode. The piezoelectric couples and the metal terminals are secured together by a bolt. The transducer exhibits various combinations of resonant frequencies in its impedance-frequency characteristic as determined between various combinations of the electrodes and terminals.

What is claimed is: 
     
       1. A multi-frequency ultrasonic transducer comprising three couples of piezoelectric elements having respective terminals between contact faces thereof, and metal terminals being provided in respective both ends of said three couples of piezoelectric elements, said three couples of piezoelectric elements respectively arranged at the positions of about 0.125, 0.25 and 0.5 from one end in total length thereof, said three couples of piezoelectric elements and said metal terminals being fixed by a bolt which is passed through the center thereof. 
     
     
       2. A multi-frequency ultrasonic transducer according to claim 1, wherein one of said three couples of piezoelectric elements is driven by a variable frequency power source. 
     
     
       3. A multi-frequency ultrasonic transducer according to claim 1, wherein two couples of said three couples of piezoelectric elements are driven by a variable frequency power source. 
     
     
       4. A multi-frequency ultrasonic transducer according to claim 1, wherein said three couples of piezoelectric elements are driven by a variable frequency power source. 
     
     
       5. A multi-frequency ultrasonic transducer, comprising: a first piezoelectric couple comprising two piezoelectric elements each having substantially parallel inner and outer major surfaces, and a first electrode disposed between and in electrical contact with the inner major surfaces of both piezoelectric elements of said first couple;   a first metal terminal having an end face and another face opposite said end face, said other face being contiguous with one outer major surface of said first piezoelectric couple;   a second metal terminal having opposite faces, one of said faces being contiguous with the other outer major surface of said first piezoelectric couple;   a second piezoelectric couple comprising two piezoelectric elements each having substantially parallel inner and outer major surfaces, and a second electrode disposed between and in electrical contact with the inner major surfaces of both piezoelectric elements of said second couple, one of said outer major surfaces being contiguous with the other face of said second metal terminal;   a third metal terminal having opposite faces, one of said faces being contiguous with the other outer major surface of said second piezoelectric couple;   a third piezoelectric couple comprising two piezoelectric elements each having substantially parallel inner and outer major surfaces, and a third electrode disposed between and in electrical contact with the inner major surfaces of both piezoelectric elements of said third couple, one of said outer major surfaces being contiguous with the other face of said third metal terminal; and   a fourth metal terminal having an end face and another face opposite said end face, said other face being contiguous with the other outer major surface of said third piezoelectric couple,   said piezoelectric couples and said metal terminals being secured together,   whereby the electrical impedance of said transducer exhibits various resonant frequencies between various combinations of said electrodes and metal terminals.   
     
     
       6. The transducer according to claim 5, wherein the distance between said third electrode and the end face of said first terminal is substantially equal to one-half the distance between the end faces of said first and fourth terminals, the distance between said second electrode and the end face of said first terminal is substantially equal to one-quarter the distance between the end faces of said first and fourth terminals, and   the distance between said first electrode and the end face of said first terminal is substantially equal to one-eighth the distance between the end faces of said first and fourth terminals.